Fourier Optics for the Analysis of Distributed Absorbers Under THz Focusing Systems

An analytical spectral model able to accurately and efficiently characterize absorbers distributed in the focal plane of focusing THz systems is presented. The model is obtained by using a Fourier optics representation of the electromagnetic field in the focal plane in conjunction with a recently developed equivalent network representation for the interaction of plane waves with distributed absorbers. The model is validated by comparisons with numerical full-wave simulations. Finally, the model is used to design a few architectures based on lens-coupled Kinetic Inductance Detectors (KIDs), which show high absorption efficiency over a large bandwidth.